There are various input devices (other than the cursor keys of a manual keyboard) which are known for positioning or controlling the movement of a cursor on a computer display screen. One of the more common in use is the conventional "mouse" device, in the form of a hand-sized housing which is moved over a flat desktop. Motion over the desktop is sensed by means of a mechanically rotating ball or optically reflective sensor, and digital data are generated which translate into corresponding motion of the cursor on the display screen. Other cursor positioning devices include the joystick, the graphics input tablet, consisting of a flat sensor pad and a hand-held pointing stylus, which translates the analog motion of the pointing stylus into digitized data used to control the location of the cursor on the display screen. Still other cursor movement devices rely on focused light sources, held by the user or fixed on the user's person, as on a pilot's helmet. As the user aims the light beam, sensors mounted around a display screen track the movement of the beam and translate this movement into a corresponding movement of the cursor on the display screen.
Devices such as those discussed above are basically effective, although they suffer from certain disadvantages. Most cursor positioning and controlling devices require a fixed, generally level surface upon which to operate, or must operate in conjunction with a stationary sensor of some type; that is, motion is sensed with respect to a fixed medium and positional data signals are generated and presented to a computer for translation into a corresponding cursor movement. The need for a fixed surface or stationary sensor constrains how the user may interact with the display device. The user must normally sit close to the display screen and be provided with ample level desk space for placement of the graphics tablet or movement of the "mouse." In the case of the stationary sensor, the user must confine movement to keep the light beam within range of the sensor array and aimed appropriately.
Still another disadvantage of many present-day cursor movement devices is that they require a level of manual dexterity for their effective use. This requirement has its greatest impact in the area of the physically disabled. To operate a computer, a disabled person may find that a mouse, a graphics tablet, or even a keyboard is useless to him.
Disadvantages of the prior art devices, such as the requirements of a flat desktop, aiming of a light source, or the manual dexterity of the user, were overcome in U.S. application Ser. No. 07/267,413, filed Nov. 4, 1988 and assigned to the assignee of the present invention. The cited application discloses an input device which does not require manual control, and which can be used by a physically disabled person.